I've got a Craftsman 30 gallon vertical air compressor that I can't get the drain valve to seal. No matter what position it is in it will still leak air. I looked at the parts diagram and it only shows a metal drain valve but my question is should there be a rubber washer on this valve somewhere? I unscrewed the valve entirely out and there is no kind of rubber seal anywhere on it. I tried putting thread compound on the threads and screwing it back in but still leaks. My hunch is the rubber seal pulled off inside the tank but does anyone know for sure? I'm about 20 miles from the nearest Sears and with the price of gas and all.......

Are the threads tapered (pipe threads?). If so, just buy a petcock and replace it with that. If they are not, you will have to find something that works or have a coupling welded into the tank so you can use pipe threads.

1967 Marina Blue Malibue with 327 and 427 on the way. Father/Son project.

My Craftsman has a cheap petcock with tapered seat (works like a brake bleeder), there's no other seal as far as I know. Looks kind of like those cheap, flimsy things you see on old radiators. It's not leaking (yet...), but I'm more afraid that it will stick and break one day. I have some ball valves that I think will be more reliable, just haven't put one on yet.

I have the same problem on my 60 gallon craftsman "professional". I havent had a chance to un-wire it and flip it over, but I'm pretty sure the valve is just junk. I will probably try to replace it someday, but at least for now it lets the water get out of there on its own!

I do repair on CH compressors, I see some other brands as well.
If the valve is leaking, all you can do is replace it.
If it's the tank/valve threads, it "should" be 1/4 npt thread (pipe), use teflon tape, or liquid thread sealer.
If it's some goofy custom straight thread, thread sealer won't work.
Try a new copper or nylon washer.

One option I totally forgot about is that new 1/4-turn, self-cleaning ball valve they sell now as water stops for sinks. I just replaced the faucet on our bathroom vanity, and as the water stops crapped out (not totally unexpected... ) when I tried to close them, I replaced them with this new type. They were really neat, compared to the old style that always seems to malfunction in one way or another. We'll see how they hold up in the long run, but they seem to be good quality pieces and come as straight or angled. Don't know about the pressure rating, but they might work for a compressor as well.

BTW: Why is it that the water stops always take a crap before the faucets? They are there to make it possible to replace a faucet without shutting off the main supply line, but you always end up shutting the main line and replacing or repairing the water stops when you replace a faucet anyway. And IMO, they are more cumbersome to replace than the faucet itself. Sorry, I know that it's off topic, just needed to get it off my chest.

On my shop compressor I run an elbow and some pipe out to an easy access
and have two stainless ball valves in line for draining water. Completely
leak free and simple draining. You probably don't need two on a smaller home unit.

I think something like a rubber washer must have come off the drain valve because when I turn it clockwise to close the valve it will continue to screw all the way out until it falls out of the tank! And I'm sure this isn't supposed to happen. I'll be headed to Sears to get a new valve. I checked online and it's a $4.93 part but would cost me an extra $5.99 to ship it! Sure hope I didn't break something inside the tank and it will always leak but that would be my luck! It seems to work fine turning it counter clockwise as the drain valve screws into the tank and I can feel all the air coming out of the hole in the valve but when I turn it clockwise to close it the thing never hits a sweet spot where air doesn't come out the hole or the threads although it's difficult to tell where the air is coming from. But the dang thing unscrews all the way out which doesn't seem right.